Apparatus for varying time delay in electron drift tube by velocity modulating electron beam



Apnl 11, 1967 J. B. PAYNE m 3,

APPARATUS FOR VARYING TIME DELAY IN ELECTRON DRIFT TUBE BY VELOCITY MODULATING ELECTRON BEAM Filed Sept. 4, 1964 ACCELERATING ANODE OUT u-r SIGNAL INVENTOR. JOHN B PAYNE nr BY u/HAA I 4 mt fwk A ATTORNEYS.

DRIFT REGION FlG 5 m m T T m m m T C u 6 b O O l L O O 5 o I. c \u/ A v I r0 0 2 H a z N S 6 I. :0 AM 6 N 1 fim IA R0 AW mA E M V :CA 0 E" :R -2 ADZRM in 6 AA 3 MW m i En I s :R EE MHRB F E x L 0 c M 5 D E fiP- E m c F m w A A. n A l l A N G I. D N AIIY up". I L OIYIW u j E H R f WA N w I v 3 A L T l PW A I. I M E UP N- m I E n m c mm H A :Ts n w l V Ml lku; IV H c IF n AP M t M E o c o l 1 c w H I c H A A C A C United States Patent 3,314,016 APPARATUS FOR VARYING TIME DELAY IN ELECTRON DRIFT TUBE BY VELOCITY MODU- LATING ELECTRON BEAM John B. Payne III, Westernville, N.Y., assignor to the United States of America as represented by the Secretary of the Air Force Filed Sept. 4, 1964, Ser. No. 394,639 3 Claims. (Cl. 328-433) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to an apparatus for velocity modulating an electron beam and more particularly, to velocity modulating an electron beam to obtain a variable time delay.

The purpose of this invention is to produce a variable or adjustable time delay up to 50 nanoseconds of a wideband radio frequency signal. Such a signal might be a pulse within a radar system. A variable time delay capable of handling wideband signals would greatly improve the performance of array type radars. Variable time delays of this type might also be used to improvesignal and data processing techniques.

In accordance with the present invention variable time delay is obtained by controlling the propagation velocity of an electron beam between two points in a drift tube. The signal to be delayed is coupled to the electron beam at the electron gun end of the 'drift tube. The time required for this signal to reach an output coupler also located in the drift tube is inversely proportional to the beam velocity. The beam velocity can be controlled by allowing the electrons to pass through an acceleration potential whose magnitude may be varied. The velocity and thus the time delay varies in accordance with the variation of aforesaid acceleration potential.

An object of the present invention is to provide an apparatus for obtaining a variable time delay by velocity modulating an electron beam.

Another object of the present invention is to provide an apparatus for obtaining a variable time delay by controlling the propagation velocity of an electron beam between two preselected points thereof.

The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention and methods of operation, together with further objects and advantages thereof, may best be understood by reference to the following description When taken in connection with the accompanying drawings wherein:

FIGURE 1 illustrates a simplified schematic diagram of the present invention;

FIGURE 2 shows a schematic diagram of a preferred embodiment of the present invention; and

FIGURE 3 shows a schematic diagram of another preferred embodiment of the present invention which provides time delay and amplification simultaneously.

Now referring in detail to FIGURE 1 which is a simplified schematic diagram of an electron discharge device wherein electrons emitted by cathode are accelerated or velocity modulated toward acceleratinganode 11 by potential V supplied by variable power source 12. The electrons pass through slot 13 of anode 11 and form a beam with a velocity v as determined by the magnitude of potential V Anode 11 and collector 16 are interconnected. They are thus at the same potential. The electron beam will propagate through the drift region toward collector 16 at the constant velocity, v The drift region may be such as described in the drift tube of US.

Patent No. 3,012,170 issued Dec. 5, 1961. Anode 11 and collector 16 may be such as shown and described in US. Patent No. 2,997,615 issued Aug. 22, 1961. A magnetic field, H, may be supplied in the conventional manner which is parallel to the direction of propagation to hold the electrons in the desired pencil beam.

As the beam passes through signal input coupler 14, input signal energy is coupled to the beam by punching the electrons in packets. The packets or bunched electrons continue toward collector 16 at a constant velocity. Energy is removed from the beam at output coupler 15. The time delay between input coupler 14 and output coupler 15 is inversely proportional to the electron beam propagation velocity (assuming constant spacing of coupler-s). Thus, by varying the accelerating potential, V the electron beam velocity is varied producing the variable time delay. That is, increasing V increases v the electron beam velocity. Therefore, the time delay between input and output couplers is decreased.

If theinput and output couplers are spaced at distance X from each other and the beam velocity is v then the time delay between aforesaid couplers is given by:

T=X /v seconds The beam velocity v is related to the accelerating p0- tential V b by the expression:

Here e/m is the electron charge to mass ratio. The above equation becomes:

The change in time delay, AT, produced by varying the accelerating potential from V to V can be written as:

aF JW] Now referring to FIGURE 2 which illustrates a preferred schematic configuration utilizing the basic principle shown in FIGURE 1, the most efiicient coupling between coupler and the electron beam occurs when the beam velocity and wave propagation velocity of the coupler are approximately the same. For this reason it is desirable to maintain a constant beam velocity in the coupler region for all values of beam velocity, v in the drift region, X,,. This is accomplished by the addition of four anodes 1'8, 19, 20 and 21. Potential V supplied by battery 17 which is connected between cathode 10 and anode 11 accelerates the electron beam to the desired coupling velocity, v The electron beam drifts through the coupling region (between anodes 11 and 18) at a constant velocity, where input signal energy is coupled onto the electron beam by input coupler 14 to the desired coupling velocity, v Between anodes 18 and 19 the beam is velocity modulated to the desired velocity, v by the accelerating potential, V which is provided by variable power source 12. Magnetic field, H, parallel to the direction of the electron beam is applied to hold the electrons in a pencil beam through the drift region. Anodes 20 and 21 decelerate the beam velocity through the same potential it was accelerated between anodes 18 and 19. The beam velocity has now been returned to the proper value for coupling energy from the beam to output coupler 15 to provide an output signal which represents the input signal with a time delay imposed thereupon. If the region between anodes is small compared to X the drift region, then the preceding equation-s also hold for the time delays provided by the embodiment shown in FIGURE 3.

It is to be noted that each input coupler 14 and output coupler 15 may be a helix type such as utilized in a traveling wave tube or in some instances may be such .as utilized in a Klystron device known as buncher and catcher cavities, respectively. Magnetic field, H, and anodes 13, 18, 19 and 20 may be of the type shown and described in the aforementioned US Patent No. 2,997,615.

The preferred embodiments shown in FIGURE 2 provides no gain or amplification of the delayed signal. If gain is desired then the embodiment illustrated in schematic form of FIGURE 3 may be utilized wherein output coupler 15 may be constructed in the form of extended helix 22 of length L with the actual output coupler 15 at the collector end of the helix. The device illustrated in FIGURE 3 would then resemble a traveling wave tube. Interaction between the electron beam and a helix would provide the required amplification of the delayed signal.

What I claim is:

1. Apparatus to provide a variable time delay by controlling the propagation velocity of an electron beam in an electron discharge device comprising means to form .an electron beam in said electron discharge device, first means to accelerate said electron beam to a first preselected velocity, means to couple an input signal to be delayed onto said electron beam subsequent to accelerating said electron beam to said first preselected velocity, second means to accelerate said electron beam to a second preselected velocity subsequent to said input signal coupling operaiton, said second means being variable, a drift region having a predetermined distance through which said electron beam passes after attaining said preselected second velocity, said predetermined distance and said preselected second velocity determining said time delay, means to hold the electrons passing through said drift region in a pencil beam, means to decelerate said electron beam after passage through said drift region to said first preselected velocity, and means to couple out the input signal from said electron beam after said decelerating operation.

2. Apparatus to provide a variable time delay as described in claim 1 wherein said second variable means includes a variable power supply, and wherein said electron beam from said electron beam forming means to said output coupling means is a straight path.

3. Apparatus to provide a variable time delay as described in claim 1 wherein said output coupling means is comprised of a first helix coupled to a second helix, said electron beam after said deceleration interacting with said first and second helices to provide amplification of the delayed input signal.

References Cited by the Examiner UNITED STATES PATENTS 2,414,843 1/ 1947 Varian et a1. 328228 2,508,228 5/1950 Coeterier 328233 2,774,008 12/1956 Rooks 328177 3,225,314 12/1965 Rambo 328177 DAVID J. GALVIN, Primary Examiner.

ARTHUR GAUSS, J. S. HEYMAN,

Assistant Examiners. 

1. APPARATUS TO PROVIDE A VARIABLE TIME DELAY BY CONTROLLING THE PROPAGATION VELOCITY OF AN ELECTRON BEAM IN AN ELECTRON DISCHARGE DEVICE COMPRISING MEANS TO FORM AN ELECTRON BEAM IN SAID ELECTRON DISCHARGE DEVICE, FIRST MEANS TO ACCELERATE SAID ELECTRON BEAM TO A FIRST PRESELECTED VELOCITY, MEANS TO COUPLE AN INPUT SIGNAL TO BE DELAYED ONTO SAID ELECTRON BEAM SUBSEQUENT TO ACCELERATING SAID ELECTRON BEAM TO SAID FIRST PRESELECTED VELOCITY, SECOND MEANS TO ACCELERATE SAID ELECTRON BEAM TO A SECOND PRESELECTED VELOCITY SUBSEQUENT TO SAID INPUT SIGNAL COUPLING OPERATION, SAID SECOND MEANS BEING VARIABLE, A DRIFT REGION HAVING A PREDETERMINED DISTANCE THROUGH WHICH SAID ELECTRON BEAM PASSES AFTER ATTAINING SAID PRESELECTED SECOND VELOCITY, SAID PREDETERMINED DISTANCE AND SAID PRESELECTED SECOND VELOCITY DETERMINING SAID TIME DELAY, MEANS TO HOLD THE ELECTRONS PASSING THROUGH SAID DRIFT REGION IN A PENCIL BEAM, MEANS TO DECELERATE SAID ELECTRON BEAM AFTER PASSAGE THROUGH SAID DRIFT REGION TO SAID FIRST PRESELECTED VELOCITY, AND MEANS TO COUPLE OUT THE INPUT SIGNAL FROM SAID ELECTRON BEAM AFTER SAID DECELERATING OPERATION. 